The present invention relates to the field of high intensity discharge lighting, and in particular to a gas discharge lamp subject to arc instability due to acoustic resonance.
Gas discharge lamps, generally understood as a family of illumination devices such as fluorescent, sodium, metal halide, mercury and others are commonly used sources of illumination. The term HID is generally understood as a family of high intensity discharge illumination devices within the full spectrum of gas discharge devices. U.S. Pat. No. 5,883,475 defines the prior art and issues surrounding their operation at high frequencies exceptionally well as detailed below within the prior art section.
It is well known that the efficiency of gas discharge lamps is generally improved by operating such lamps by means of high frequency electrical input power to drive the discharge within the lamp. However, high frequency operation of relatively short lamps introduces the potential generation of acoustic compression waves in resonance with the natural acoustic frequencies of the lamp. It is also well known that the natural acoustic frequencies are affected by the variation of operating parameters including lamp lifetime and temperature.
The use of alternating current (AC) to power a gas discharge introduces a time-varying application of electrical power to the electrodes of the lamp. This time-varying application of electrical power generates variations in the gas through which the electrical discharge occurs. The alternative attraction and repulsion of electrons (and corresponding repulsion and attraction of positive ions) from a discharge electrode causes pressure variations in the gas in the vicinity of the electrodes that generates local regions of compression. Such pressure variations created in the vicinity of a discharge electrode will typically propagate into the gas of the lamp as an xe2x80x9cacoustic wavexe2x80x9d or an xe2x80x9cacoustic compression wavexe2x80x9d. Thus, these acoustic waves are an inherent and unavoidable consequence of driving the electrical discharge by means of alternating positive and negative voltage being applied to the discharge electrodes.
When the discharge-induced acoustic compression waves occur at the natural acoustic frequencies of the HID lamp, acoustic resonance occurs. The phenomenon of acoustic resonance essentially generates standing pressure waves within the HID tube. Such waves can cause the light from the lamp to flicker; cause the arc within the tube to warp, bend or become extinguished; or in extreme cases cause the arc to contact the walls of the HID lamp and damage or destroy the tube itself. Even modest variations in spacial or temporal light intensity are unacceptable in many applications of HID lamps in which focusing of the light is necessary. Other deleterious effects of acoustic resonance may considerably shorten the service lifetime of the lamp.
The precise frequencies at which acoustic resonance occurs are a complex function of the composition, temperature and pressure of the gas within the HID tube, and the geometry of the tube itself. In addition, the composition, temperature and pressure of the gas varies from place to place within the tube, being typically hotter and less dense near the center of the arc while cooler and more dense near the walls of the tube. Adding further to the complexity of acoustic resonance is the fact that the properties of the tube and the gas are not constant over time. Tube electrodes will typically change their geometry over the lifetime of the lamp as they are subjected to numerous hours of electrical discharge and bombardment by ions, electrons and neutral species from the gas of the HID tube. The composition of the gas will similarly change over time as chemical processes within the HID gas proceed over many hours of operation. Practical manufacturing tolerances also lead to variations in tube geometry from lamp to lamp, even when new. All these factors accumulate so as to make it exceedingly difficult to predict with any reasonable precision the acoustic resonance frequencies of a particular HID tube, or to predict how such acoustic resonance frequencies will change over the service lifetime of the lamp. In general, acoustic resonance frequencies tend to occur in the range above about 10 KHz for typical HID lamps, increasing thereby the complexity in obtaining efficient, high frequency operation of such lamps.
Several past attempts have been made to avoid acoustic resonance and to sweep through the acoustic resonance frequency to avoid the accompanying instability of the gas discharge arc when the operating frequency approaches the natural acoustic frequencies of the lamp. Only U.S. Pat. No. 5,680,015 titled xe2x80x9cMethod to operate a discharge lamp, and circuit arrangement for operation of the discharge lampxe2x80x9d of Bernitz et al discloses the utilization of a testing phase comprised of discrete stepping frequencies to determine the stable region of operation. Bernitz subsequently utilizes a single frequency within their designated stable frequency range for lamp operation.
In contrast to much of the prior art, the present invention is not based upon a ramp sweeping through acoustic resonant frequencies of the particular gas discharge lamp. Rather, the present invention utilizes discrete modulation frequency steps. In carrying out the efforts that resulted in the present invention, it was discovered that the operation of the drive signal in conjunction with a discrete modulation step frequency in the acoustic resonance band could provide the desired arc stability.
None of such patents relate to the use of discrete modulation frequency steps to improve output stability. In contrast, the present inventors have developed a new operational method and system using discrete modulation frequency steps in the operation of a gas discharge lamp to provide improved photometric characteristics regardless of lamp orientation. The present invention provides a new, optimal and low cost operational method of use and system, which achieves superior performance over the above-referenced prior art, and others.
In accordance with one aspect of the present invention, a discrete modulation ballast operation is provided. The operation includes the periodic cycling of multiple individual frequencies to drive a gas discharge lamp with arc stability. In accordance with yet another aspect of the present invention, a microprocessor is provided to control the discrete modulation ballast operation. The operation includes the start-up, re-strike, dimming, and communications procedures to drive a gas discharge lamp. In accordance with another aspect of the present invention, a discrete modulation ballast dimming operation is provided. The operation includes an incremental step increase of frequency of the periodic cycling of full power multiple individual frequencies that drive a gas discharge lamp. In accordance with another aspect of the present invention, a R-C circuit is introduced to delay and eliminate the overlap of two out-of-phase square waves is provided. In accordance with yet another aspect of the present invention, a dynamic feedback method is provided. The operation includes the feedback method of actively modifying the discrete frequency steps.
As used herein, the lighting system is used to imply the collective ballast and lamp components.
As used herein, processor requirements are used to imply the microprocessor digital pulse output and processing speed to support the ballast""s operations.
As used herein, the term discrete is used to imply a discontinuous step function of multiple individual frequencies that switch steps at a fixed time interval.
As used herein, the term microprocessor programs is used to collectively encompass the control algorithms utilized throughout the entire range of lighting system""s operations. The lighting system""s operations include arc striking during start-up, arc re-striking following lamp operation, continuous dimming operation, discrete multi-level dimming operation, light level maintenance operation, and other strategies as determined by an energy management system.
As used herein, the term energy management system is used to collectively encompass an overall strategy of multiple lighting systems within a physical structure (e.g., building, home, etc.). The overall strategies include real-time day lighting control, occupancy sensing control, time scheduled light level control, demand load shedding control, real-time demand light level control, and other control algorithms.
As used herein, the term acoustic resonance is the phenomena of a frequency or range of frequencies associated therewith and which occurs within the arc tube of a discharge lamp in conjunction with the excitation of the gases contained within the arc tube. The acoustic resonance condition is one wherein periodic oscillations in pressure occur in phase with the amplitude-modulating component of the input power thereby producing standing pressure waves.
An advantage of the present invention is to provide a method to operate a gas discharge lamp with solid-state ballast that provides for stable and flicker-free operation by minimizing acoustic resonance. A method to operate a gas discharge lamp with solid-state ballast provides for a stable, flicker-free operation throughout its entire continuous dimming range. Another advantage of the present invention is to provide a R-C circuit method to reduce the processor requirements of the microprocessor and subsequent cost of the lighting system. Another specific advantage of the present invention is to provide an active method to further enhance the stability of the gas discharge lamp for flicker-free operation. Other advantages of the present invention derive from the microprocessor programs to achieve the desired power and lumen levels in accordance to energy management system directives.
Additional features and advantages of the present invention are described in and will be apparent from the detailed description of the presently preferred embodiments. It should be understood that various changes and modifications to the presently preferred embodiments described herein will be apparent to those skilled in the art. Such changes and modifications can be made without departing from the spirit and scope of the present invention and without diminishing its attendant advantages. It is therefore intended that such changes and modifications be covered by the appended claims.